These factors could effect the rate of reaction on an enzyme:
· pH
· Concentration
· Temperature
· Surface Area
pH - Enzymes function at different pH values. In neutral conditions the amount of oxygen gas given of in an enzyme-catalysed reaction will increase.
An enzyme is affected by how much acid or alkali is present. Many enzymes work best in neutral conditions but some prefer acids and some prefer alkalis.
This graph shows that the enzyme activity reacts best at pH7 (neutral)
Concentration - In concentrated solution there are more collisions between each particle, so the reaction occurs more quickly.
This graph shows that increasing the concentration increases the enzyme activity.
Temperature - Reactions go faster as temperature rises. The rate of reaction also increases as the temperature rises, but with enzyme-catalysed reactions the reaction rate starts to decrease when the temperature is above 40 C. This is because enzymes are proteins and their structures start to damage above 40 C.
This graph shows that the enzyme activity reacts best at 40°C as the enzyme starts to denature above 40°C
Surface Area - Reactions can react faster when solids are cut into smaller pieces. This is because there is more surface area which is exposed.
The more surface area there is, the more collisions that take place between particles so the reaction rate is much quicker.
This graph shows that small pieces react better than bigger pieces.
Enzymes
A catalyst is the name given to something, which speeds up a chemical reaction but does not take any part in the reaction. The catalyst can be recovered once the reaction is over. Biological catalysts are the name given to catalysts in living cells. These are called enzymes and they are all protein molecules. An enzyme is specific, which means that it will only accelerate one particular reaction. One of the most well known enzymes is called salivary amylase. Most enzymes work by bringing the chemicals, which are reacting closer together on the surface of the enzyme.
Brief Outline
I will test the effects of changing the level of concentration. For this variable I will use three different concentrations of hydrogen peroxide with catalase (enzyme). I will change the concentration whilst keeping the time, concentration of catalase and the volume of hydrogen peroxide constant.
I will begin all my tests at a constant temperature (room temperature) and I will repeat each test three times so I can obtain an average result.
Background Knowledge:
Lock and Key Model
A catalyst is a substance which alters the rate of reaction without being used up. Enzymes are the catalysts in biological processes. They are large proteins that speed up chemical reactions. The enzyme forms the active site from small numbers of amino acids.
The active site is the location on the enzyme where the substrate collides and the reaction takes place. If the shape of and the substrate do not match exactly then they do not bind. This makes sure that the enzyme does not work with the wrong reaction.
Enzymes are not affected by the reaction, so when the products have been released, the enzyme is ready to bind with a new substrate.
In my experiment the substrate was the hydrogen peroxide, the enzyme that we used was hydrogen peroxide and the product that was formed was oxygen and water.
This can be explained by an equation:
Enzyme + Substrate Þ Product
In my experiment this is shown as:
Catalase + H202Þ H202 + 02
This equation explains how the catalase in our experiment binded with the H202 to break it down and form oxygen.
Induced Fit Theory
The induced fit theory states that the binding of a substrate to an enzyme causes a change in the shape of the enzyme.
The enzyme and the substrate act on each other to affect the making of the active site to the usual complex between the enzyme and its substrate. As a result, this means the enzyme to catalyze a reaction has changed.
This shows that enzymes are specific for specific substrates.
I can tell that the catalase in my experiment is a suitable enzyme to break down the H202 as it will form oxygen as a product which is unharmful
Denaturing
Denaturing is the damage to the protein structure of an enzyme. Most enzymes react faster as the temperature increases. Enzymes also react at low temperatures, but when the temperature rises above 40 C their reaction rate start to decrease. This is because enzymes are proteins and their structures get damaged when the temperature rises above 40 C.
When the protein is denatured it becomes less effective as a catalyst and soon the enzyme reaction gets slower and then finally it stops.
This is why enzymes in washing powders which clean by breaking down grease and other stains, cannot be used with hot water above 40 C
Activation Energy
In order for a reaction too occur activation energy must be supplied.
The activation energy is the energy required to start a chemical reaction.
Some elements and compounds react together to bring themselves into contact. For others it is necessary to supply energy in order to start the reaction. This energy is the activation energy.
Enzymes such as catalyst work by lowering the activation energy.
The Kinetic Theory of Matter
Everything is made of moving particles. The main points of the kinetic theory are:
· All matter is made up of small particles called molecules
· The molecules are always vibrating
· The higher the temperature, the faster the molecules are moving
· As the temperatures rises the particles get hotter. They have more energy and move around faster.
Solid Liquid Gas
Solid - In a solid the particles are very close together and have very strong forces between them. Solid particles can only vibrate, this is why they cannot flow. Solids have a fixed shape and a fixed volume
Liquid - In a liquid the particles are a little further apart. The forces are not very strong. Liquids can flow and change shape but they always have a fixed volume.
Gas - In a gas the particles are further apart. There are no forces to hold all the particles together. Thy move about very quickly in the space they find. Gases can flow easily and change their shape and their volume depending on the container.
Collision Theory
The collision theory explains chemical reactions and the way in which the rate of reaction alters when the conditions alter.
For a reaction to occur the reactant particles must collide. Only a fraction of the total collisions cause a chemical change. These are called fruitful collisions. The fruitful collisions have sufficient energy (activation energy) to break the existing bonds and to form new bonds, which then form the products of the reaction.
Increasing the concentration of the reactants and raising the temperature make more collisions and therefore more fruitful collisions which increases the rate of reaction.
All reactions involve two reactants which need collisions between them for particles to proceed. But not all collisions taking place between particles end up with a reaction. This is because in the middle of a reaction, there is a shape of the particle which is difficult to complete. This is called the transition state.
The total kinetic energy of reactant molecules must be at least as high as the activation energy to be able to achieve the transition state, so the reaction can proceed.
For a reaction to occur there must be successful collisions in which:
1) Particles must collide
2) Particles must have enough energy for the reaction to take place (activation energy). Which means the reaction must be successful
If a collision between particles can produce sufficient energy and the particles collide fast enough in the right direction a reaction will take place. But not all collisions result in a reaction.
A reaction is speeded up if the number of successful collisions are increased.
The particles in a If the collision has If the collision does not
liquid move around enough energy a have enough energy no
continually reaction takes place reaction occurs
The rate of reaction depends on how many successful collisions there are in a given unit of time.
Surface area
By breaking solids into smaller pieces the surface area is increased, which gives a greater area for collisions to take place. This causes an increase in the rate of reaction.
Temperature
When a substance is heated, the particles move faster. When the particles are moving faster they will travel at greater distances which will involve more collisions. This will increase the rate of reaction.
Concentration
The more concentrated the reactants are the greater the rate of reaction. This is because increasing the rate of reaction increases the number of collisions between particles and therefore increases the rate of reaction.
Pressure
An increase in pressure can lead to an increase in the rate of reaction. The increase in pressure forces the particles closer together. This causes more collisions and therefore increases the rate of reaction
We are going to record our results. This is how my table will look:
Method
After choosing the selection of apparatus and making a prediction. I must now draw up a plan to test my theory. But first and foremost I must clarify which variables are to be controlled and which variables is to be changed.
As I have mentioned before the variable to be changed each time is:
So therefore the variable I will keep constant are:
-Amount of hydrogen peroxide
- Temperature of the hydrogen peroxide
- Concentration of the hydrogen peroxide
- Mass of the piece of potato
- Type and age of the potato
- Apparatus used
The above list of controlled variable will ensure I have a fair test to give accurate results. And I will repeat the experiment again to make sure.
So to sum it up the variables, what will be measured, is due to the change surface area.
Thus I have made a plan set fourth in accordance to all the information above:
- Collect all the right apparatus.
- Set the experiment in a free space zone area.
- Cut the potatoes to the various sizes from the received 4cm potato.
- Measure out 20cm3 of hydrogen peroxide by using a measuring cylinder.
- Receive test tube and pure in the hydrogen peroxide and the various potato sizes.
- Wait for four minutes.
- Then get a ruler.
- Measure the length of the froth.
- Afterwards, dispose of the potato into a bin, and clear the surfaces you have worked on.
- Repeat for all left sizes.
This is the method I am going to use for every potato size.
By carrying out all the things, which I have listed, I will be able to establish precisely that my test has been fair. I will be able to prove this by saying all materials and apparatus have been handled and used with the same treatment, and in an overall fair manner.
Bibliography
In aiding me in the preliminary work I have done and general secondary source of information, I used the following books with author(s) beside them:
- - I looked for this on a search engine, and it was a very useful site. There was a lot of detail that helped me with my notes, and it had links to other sites.
- AS Biology Revision guide, OCR – This was very useful because I related directly to our experiment and it gave me a basis of how to set up my experiment.
- Biology 1 Advanced Studies Textbook, OCR – This was not as useful as my other sources, however there was one passage that explained about the initial rate of reaction.
OBTAINING EVIDENCE
ANALYSING
What is shown by the evidence?
The table clearly shows that as the surface area is increased the rate of reaction increases and that the reaction causes the catalyse to produce more oxygen from the hydrogen peroxide solution.
Next four pages represent graphs, which gives evidence that my prediction was valid.
Patterns and Trends:
The only trend and pattern that the graphs and table shows is that as the surface area is increased the rate of reaction increases and that the reaction causes the catalyse to produce more oxygen from the hydrogen peroxide solution.
Conclusion
From looking at the table and my graph I have observed that it has backed up my prediction. As the surface area is increased the rate of reaction increases as well as due to the enzyme catalyse speeding up the reaction by giving the reaction speed and energy. My graphs absolutely proves my conclusion is correct.
This is simply due to:
Surface area
By breaking solids into smaller pieces the surface area is increased, which gives a greater area for collisions to take place. This causes an increase in the rate of reaction.
Surface Area - Reactions can react faster when solids are cut into smaller pieces. This is because there is more surface area which is exposed.
The more surface area there is, the more collisions that take place between particles so the reaction rate is much quicker.
The biological catalyst catalyse has a lot to do with the conclusion. Most enzymes work by bringing the chemicals, which are reacting closer together on the surface of the enzyme. So this must be a cause.
Evaluating
Evaluation
I believe the experiment went well and the results are reliable as it supports my original idea of what would happen. I think my experiment has some limitations as I do not know what would happen to the reaction after fifteen minutes so I do so believe that my experiment could be improved, to do this I would take more averages to make it even more accurate and would also do it for longer and try to do it until the reaction stops and the hydrochloric acid becomes totally saturated. I think this would show further that the reaction slows down after time.
Improvements
- Used larger potatoes to start with.
- Work in a spacious area were there is no disturbance to ensure accurate results.
- Use a larger volume of hydrogen peroxide.
Extended enquiries
To extend the experiment the following could be carried out:
- Increasing the hydrogen peroxide volume.
- Larger surface areas.
- Use more potatoes.
- Repeated experiment more.
